1. Field of the Invention
This application is directed to a cushioning system for a shoe, and in particular, a fluid-filled bladder cushioning system containing separate reservoir chambers.
2. Description of the Related Art
Bladders have long been used in shoes as a cushion to increase shoe comfort, enhance foot support, reduce the risk of injury and other deleterious effects, and decrease fatigue. In general, the bladders are comprised of elastomeric materials which are shaped to define at least one pressurized pocket or chamber. Typically, a bladder will actually define many chambers arranged in a pattern designed to achieve one or more of the above-stated objectives. The chambers may be pressurized with a number of different mediums, such as air, various gases, water, or other liquids.
Many different chamber configurations have been developed in an effort to achieve the desired results. For instance, bladders have been constructed with a single chamber that extends over the entire area of the sole. One example of this type of bladder is disclosed in U.S. Pat. No. 2,080,469 to Gilbert, entitled "Pneumatic Foot Support." Alternatively, bladders have included a number of chambers fluidly interconnected with one another. Examples of these types of bladders are disclosed in U.S. Pat. No. 4,183,156 to Rudy, entitled "Insole Construction For Articles of Footwear," hereby, incorporated by reference, and U.S. Pat. No. 900,867 to Miller, entitled "Cushion for Footwear." However, these type of bladder constructions have been known to flatten and "bottom out" when they receive high impact pressures, such as experienced in athletic activities. Such failures negate the intended benefits of providing the bladder.
In an effort to overcome this problem, bladders have been developed wherein the chambers are fluidly connected by restricted openings. Examples of these bladders are illustrated in U.S. Pat. No. 4,217,705 to Donzis, entitled "Self-contained Fluid Pressure Foot Support Device," U.S. Pat. No. 4,129,951 to Petrosky, entitled "Air Cushion Shoe Base," and U.S. Pat. No. 1,304,915 to Spinney, entitled "Pneumatic Insole." These bladders, however, have tended to either be ineffective in overcoming the deficiencies of the non-restricted bladders or have been too expensive to manufacture.
Additionally, artisans have developed shoe bladders which include a number of separate chambers that are independent of one another. In other words, the chambers are not fluidly connected. Hence, the fluid contained in any one chamber is precluded from passing into another chamber. One example of this construction is disclosed in U.S. Pat. No. 2,677,906 to Reed, entitled "Cushioned Inner Sole For Shoes and Method of Making the Same." Although this design obviates "bottoming out" of the bladder, it also requires each chamber to be individually pressurized. Thus, the cost of production has been exceedingly high. U.S. Pat. No. 4,722,131 to Huang discloses an open system type of air cushion. The air cushion has two cavities, with each cavity having a separate air valve. Thus, each cavity can be inflated to a different pressure by pumping in or releasing air as desired. However, in systems such as disclosed in Huang, a separate pump is required to increase the pressure in the cavities. Such a pump would have to be carried by the user if it is desired to inflate the cavities away from home, inconveniencing the user. Alternatively, the pump could be built into the shoe, adding weight to the shoe and increasing the cost and complexity. Additionally, open systems tend to lose pressure rapidly due to diffusion through the bladder membrane or leakage through the valve. Thus, the pressure must be adjusted often. Furthermore, a pressure gauge is necessary to determine if the desired internal pressure has been achieved. Pressure gauges are expensive, and have limited accuracy at the low pressures and volumes which would be utilized in the cavities, due to the fact that a significant volume of air is required to register a given pressure. Thus, such a large volume of air would escape during the taking of a pressure reading that the reading would be inherently inaccurate.
Another shoe bladder manufactured by Etonic also includes a plurality of discrete chambers which lack fluid interconnection. The chambers are, however, all formed at ambient pressure. This construction obviates the need to individually pressurize each chamber and thus results in less manufacturing costs. However, the use of chambers pressurized above ambient pressure is not possible. As a result, the versatility and potential gain from using the bladder is reduced.
Attempts have further been made to design the bladders to suit specific needs. For example, the support and cushion needed for jogging would be different than that needed for aerobics. In bladders having either restricted connections between chambers or independent chambers, artisans have sought to differentiate the pressures in the various chambers depending on the part of the plantar surface to be supported and the activity to be engaged. Examples of this practice include U.S. Pat. No. 4,445,283 to Meyers, entitled "Footwear Sole Member," the '705 patent to Donzis, the '906 patent to Reed, the '951 patent to Petrosky, and the '915 patent to Spinney. These approaches, however, have not been entirely successful. With respect to the restricted flow bladders, the results have had only limited success in actually providing the desired differences in pressure. Although the independent bladders effectively provide different pressures at various points across the sole, the cost to manufacture the bladders has been prohibitively high. As illustrated in FIGS. 3 and 7 in the '906 patent to Reed, each independent chamber must be individually pressurized. As can be readily appreciated, this process is not suitable for mass production, particularly in bladders having a significant number of chambers.